else and finally | Pychallenger

A try block can have two more parts. The else clause runs only when nothing went wrong, and finally runs no matter what.

Full syntax with all four blocks:

try:
	# code that might fail
except SomeError:
	# runs only on that error
else:
	# runs only on success
finally:
	# always runs

Python

When the try succeeds, both else and finally run:

try:
	x = int("5")
except ValueError:
	print("bad")
else:
	print("ok")
finally:
	print("done")

Python

Output

When the try fails, except and finally run, else is skipped:

try:
	x = int("hi")
except ValueError:
	print("bad")
else:
	print("ok")
finally:
	print("done")

Python

Output

What will be the output?

try:
	x = 10 / 2
except ZeroDivisionError:
	print("zero")
else:
	print("ok")
finally:
	print("end")

Python

Why bother with else? It separates the code that might fail from the code that runs after success. Anything in else is guaranteed not to be caught by the except above.

With else, code that should only run on success is safely outside the try, so its errors will not be swallowed by the except above.

try:
	n = int("12")
except ValueError:
	n = 0
else:
	n += 1
print(n)

Python

Output

What will be the output?

try:
	n = int("x")
except ValueError:
	n = 0
else:
	n += 1
print(n)

Python

The finally block is for cleanup. It runs whether the try succeeded, an exception was caught, or even an unhandled exception bubbled out.

A counter that always increments:

attempts = 0
try:
	x = int("hi")
except ValueError:
	x = 0
finally:
	attempts += 1
print(attempts)

Python

Output

What will be the output?

log = []
try:
	x = 1 / 0
except ZeroDivisionError:
	log.append("err")
finally:
	log.append("end")
print(log)

Python

What will be the output?

try:
	x = int("3")
except ValueError:
	x = 0
else:
	x = x * 2
finally:
	x = x + 1
print(x)

Python

What will be the output?

try:
	n = 10
except ValueError:
	n = 0
finally:
	n = n + 5
print(n)

Python

What will be the output?

try:
	x = int("nope")
except ValueError:
	x = -1
else:
	x = 100
print(x)

Python

What will be the output?

order = []
try:
	order.append("t")
except:
	order.append("e")
else:
	order.append("o")
finally:
	order.append("f")
print(order)

Python